Sigma
A monophonic analog synth manufactured by Korg circa 1979. Like many synths of the era, the Sigma was designed for keyboard players who were not experts at patch design, which led to it being an odd cross between a string synth and a conventional monophonic synth of its era. It has two sections, the "synthe" section and the "instrument" section. Each section has a set of organ-like tablet switches which selects a particular sound. The "synthe" section architecture consists of one VCO providing a number of waveforms, each of which has its own VCA and envelope generator. Each of the white tablet switches in the center group selects a combination of waveform, octave, and envelope generator parameters. E.g., one of them selects a combination of square wave in the 16-foot octave, with an AR envelope generator. For each tablet, there is one parameter which can be varied, which is provided by a small knob above the tablet. Any combination of these can be selected at a time, and they will all sound. The "instrument" section provides hard-wired circuits which produce approximations of instrument sounds typical of the era, such as string, reed and brass sounds. Like the "synthe" section, each has one variable parameter in the form of a knob above the tablet, and any combination can be selected. An interesting black-colored tab in the "synthe" section provides for the VCO to be cross modulated by the signal from the instrument section. The mix between the "synthe" and instrument sections is controlled by a knob in the performance controls area to the left of the 37-key keyboard. This area also contains a joystick, typical of Korg synths of this vintage, which controls both pitch bend and modulation. The mix is routed through a pair of filters, a low pass and a high pass; the cutoff frequency for both of these is controlled by a second, non-sprung joystick. (Curiously, there is no provision to route any modulation to the filters within the synth, although The tablets in the leftmost section are labeled "effects", which is misleading since the Sigma has no onboard effects. (This would have been understood at the time, as almost no synths of this era had onboard effects.) Rather, these tablets and knobs control aspects of the performance controls. Two of them enable and disable pitch bend for the two sections, and control the bend range for each. Two of them control sustain and retriggering modes for the keyboard. An unusual feature for this vintage is that the keyboard has aftertouch, which is enabled by a tablet switch and its range controlled by the associated knob. Switches in the performance control section allow the aftertouch signal to be routed to pitch bend or modulation, and to control either or both of the sections. Another unusual feature is the "quarter tone" tablet, which switches the keyboard to 50% scaling, such that it plays a 24-note octave over a span of an octave and a half. The rear panel provides CV/Gate inputs and outputs, as well as an FM input for the VCO, and the aforementioned control voltage input for the filters. The Sigma was one of several Greek-letter-named synths that Korg produced in the late 1970s, with similar packaging. It is packaged in a sturdy case with attractive wood sides. Like the others, the actual model name "Sigma" appears nowhere on the case; only the name "Korg" and the actual Greek letter. The Sigma did not sell well; within two years it was replaced by the Mono/Poly. Few Sigmas remain and the ones that do command high prices on the collector's market. Category:Korg synths Category:Analog synths